A trigatron is a triggered
spark gap which is typically used in radar modulators to feed the large
pulse necessary to a magnetron. Trigatrons operate either in air or are
sealed.

It consists of three electrodes,
two of similar size, one of which has a third electrode held in a hole
drilled through its middle. The undrilled electrode is negative with respect
to the other two. The other two are normally at the same potential. When
a trigger pulse is applied to the trigger electrode it causes the main
electrodes to conduct.

Open air trigatrons could not
be used at the low pressures encountered at high altitudes. After experiments
with construction techniques and gas mixes a filling of a pressurised
argon/oxygen mixture was selected with approximately 93% argon and 7%
oxygen.